Arc striking or stabilization network having a detecting transformer and capacitor connected to the electrode



United States Patent Inventors Franz Tajbl lullach, Isartal; MaxGillitzer, Munich, Germany Appl. No. 741,065 Filed June 28, 1968Patented Dec. 29, 1970! Assignee Linde Aktiengesellschaft Wiesbaden,Germany a corporation of Germany Priority July 4, 1967 Germany No.1,615,363

ARC STRIKING OR STABILIZATION NETWORK HAVING A DETECTING TRANSFORMER ANDCAPACITOR CONNECTED TO THE ELECTRODE 17 Claims, 6 Drawing Figs.

US. (I 315/209,

315/241, 315/237.1, 328/67, 307/305, 219/69 Int. Cl 1105b 39/02, H05b39/04 [50] Field of Search 219/69C, 69?, 695; 307/305; 315/237.1, 241,209; 328/67 [56] References Cited UNITED STATES PATENTS 3,158,72811/1964 Webb 219/69 3,353,062 11/1967 Nuckolls 315/157 PrimaryExaminer-John W. Huckert Assistant Examiner-B. Estrin Attorney-Karl F.Ross ABSTRACT: A method of and a circuit for the stabilization ofelectric arcs and for the ignition of welding or plasma arcs in which azero-passage detecting transformer is connected across the alternatingcurrent input to the arc electrode system and supplies a storagecapacitor discharging upon conductivity of a breakdown device to operatea solid-state semiconductor switch (thyristor) to discharge the mainstorage capacitor and apply the pulse thereof to the arc gap just afterzero-passage in the welding alternating current or just before themaximum of the supply current is reached for ignition.

PATENTEH 05029 |97B 3 F U 1 I. E [L H S mm mm FRANZ TAJBL MAX GILLITZERINVENTOR.

ATTORNEY PATENTED HEB29I97B 3551' 741 SHEET 3 [IF 3 FANZ TAJBL MAXGIILLITZER INVENTOR.

ATTOR NEY ARC STRIKING OR STABILIZATION NETWORK HAVING A DETECTINGTRANSFORMER AND CAPACITOR CONNECTED TO THE ELECTRODE Our presentinvention relates to'a method of and a system for the stabilization ofalternating current welding arcs and for the ignition of alternatingcurrent and direct current welding arcs between a welding electrode andthe workpiece.

It has already been proposed to stabilize alternating current weldingarcs, generated between an arc-welding electrode and the workpiece, bysuperimposing a high frequency alternating current upon thesubstantially lower frequency welding current to prevent extinguishmentof the welding are at the point at which the welding current amplitudepasses through its null or zero value in each alternating'current cycle.

It appears that the high frequency voltage superimposed upon the weldingcurrent ensures a rapid reignition of the are as the current amplitudepasses through the null value (zeropassage) so that recycling of the arcis unnecessary, thereby stabilizing the are over the entire period. Ithas also been proposed to use high frequency alternating current insuperimposition upon direct current welding systems to promote ignitionof the are at the initial striking or in place of such striking. Animportant advantage of such systems is that the electrode may be within2 to 4 of the workpiece to ignite the are without any direct contact.Such high frequency current has been generated heretofore by circuitsand systems which are not free from disadvantages. For example, aproblem frequently arising in these systems is the interference of thehigh frequency generator with radio communication. Attempts have beenmade to overcome this particular disadvantage by generating one or morepulses only at the precise instant as which they are necessary, i.e. asthe welding current amplitude passes through its nullvalue, andterminating the generation of such pulses when the primary weldingcurrent is most effective. However, relatively complex switchingarrangements have heretofore been required in arrangements of this type.In addition, they have consumed energy which otherwise might have beenused for the welding operation itself. When the arrangements have madeuse of sparks or arcs to control the pulse generator, the resultingozone and nitrogen oxide have been found to adversely affect the metalparts of the apparatus unless these parts have been protected againstoxidation. As a whole, therefore, prior art techniques have notsatisfactorily dealt with the problem of stabilizing alternating currentarcs or igniting alternating current or direct current arcs of a weldingsystem.

It is, therefore, an important object of the present invention toprovide an improved method of stabilizing alternating current arcs andigniting these arcs and even direct current arcs of a welding systemwhile obviating the aforementioned disadvantages.

Another object of this invention is to provide an improved stabilizingcircuit of the character described.

Still another object of the present invention is to provide a circuitarrangement for the stabilization of alternating current welding andplasma arcs, for the ignition of such arcs and for the ignition ofdirect current arcs, which manifests minimum dissipation of the arccurrent and is of relatively simple construction but can be used withoutsubstantial modification for all of the operative modes described.

We have found that these objects can be attained by a circuitarrangement for applying pulses across the arc gap (usually between awelding electrode and a workpiece) which includes a primary storagecapacitor or other charge-storing impedance connected in a dischargecircuit with a solid-state controlled rectifier or other semiconductorswitching device which is triggered to provide a pulse with a durationof 0.8 to

20 microseconds, preferably 1 to microseconds, across the arc gap; thetriggering signal is advantageously derived from a secondary storagecapacitor whose discharge, via a voltageresponsive breakdown device, isapplied to the control element of the solid-state switch (e.g. athyristor). An important feature of this invention provides that thedischarge circuit include a step-up transformer whose primary winding isconnected in series with the thyristor and the primary storage capacitorwhile the secondary winding is connected across the and does notmaterially dissipate the welding current. As will be apparenthereinafter, the present system also ensures proper triggering of thedischarge without effecting the welding operation itself and indeed theonly drain is the insignifi'. cant drain required to operate thetriggering circuit. The significance of this will be appreciated when itis recognized that conventional pulse producing devices commonly draw 30kilowatts from the welding source whereas the present system requiresonly about 1 watt.

According to a more specific feature of this invention, the triggeringcircuit includes a detecting transformer responsive to the zero-passageof the waveform of the welding source and having its primary windingconnected across the latter together with an isolating capacitor and achoke whose functions are described hereinafter. The secondary windingof the detecting transformer is connected in series with a currentlimiting variable charging resistor I across the secondary capacitor,thereby forming the charging circuit therefor. The discharging circuitof this capacitor is formed by a time-constant network whose condenseris bridged by a bleeding resistor and is interposed between thesecondary storage capacitor and a breakdown device. The latter isrendered conductive as the voltage applied across the gap rises .uponquenching of the arc and discharges the secondary storage capacitorthrough a further current limiting resistor to form the triggeringpulse.

Advantageously, the triggering pulse released by the breakdown device,preferably a glow tube, zener diode or the like, is

applied to the primary winding of a pulsetransformer whose output sidefeeds a rectifier which,-in turn, is connected to the gate of thethyristor or, where a number of thyristors are provided in oppositelypoled orientation, to the gates thereof; in the latter case, individualrectifiers may be employed. l

Still another feature of this invention resides in the provision of acharging circuit for the primary capacitorwhich includes an isolatingtransformer whose primary winding is connected to line current between aswitch and a transformer serving as the aforementioned source. In theoutput transformer of the discharge circuit of this capacitor, a diodeis placed in shunt across the primary winding and is poled oppositely tothe semiconductive switch.

The above and other objects, features and advantages of the presentinvention will become more readily apparent from the followingdescription, reference being made to the accompanying drawing in which:

FIG. 1 is a schematic diagram of a circuit for the stabilization of analternating current welding arc;

FIG. la is a fragmentary of an alternative current;

FIG. 2a is a graph (voltage amplitude plotted along the ordinate againsttime along the abscissa) showing the voltage developed between electrodeand workpiece during the process;

FIG. 2b is a graph of another voltage relationship;

FIG. 3 is a graph of the no-load source voltage of the alternatingcurrent for the welding process; and

FIG. 4 is a circuit diagram showing the application of the presentinvention to the ignition of a direct current welding arc.

' GENERAL DESCRIPTION In FIG. 1 we'show a basic circuit for control ofthe welding current applied across the welding electrode 3 which isspaced from the workpiece 2 across the arc-welding gap 2a. The systembasically comprises-a welding current source 1, a pulse generator 4 anda control circuit 5 for triggering the pulse generator. The weldingcurrent source 1 is energized by the line source 6 of 50 or 60-cyclealternating current and includes a double-pole single-throw switch 7connected between the source 6 and a welding transformer 8 of thestepdown type. The switch 7 is connected to both sides of the primarywinding of this transformer. The welding 'current may be adjusted by avariable inductance represented at 9 (e.g. a saturable reactor or anadjustable auto transformer, the inductance 9 being connected in serieswith a surge-suppressing filtering capacitor 10.

Between the switch 7 and the primary winding of transformer 8, weconnect the pulse generator 4 to the line current network via anisolating transformer 11 whose secondary winding 11a is connected to theinput terminals of afull wave rectifier bridge 12. A smoothing networkconsisting of a pair of filer capacitors 16 and 17 is bridged across theoutput terminals 12a and 12b of the rectifier 12; a resistor 14 and achoke 15 is provided between the bridge 12 and a storage capacitor 13from which the pulse energy is derived. Choke 15 acts as acharge-controlling impedance in the charging network of the capacitor 13and also serves to limit reverse current surges while resistor 14 actsas a smoothing impedance together with the smoothing capacitors '16 and17 of the filter.

The discharge circuit in which the capacitor 13 is connected includes afreewheeling 21 poled oppositely to a silicon (solid 'state) controlledrectifier or other controllable semiconductive switch device asrepresented by the thyristor 20, the rectifier diode 21 and thecontrolled rectifier being connected in series with a variable resistor18 across the capacitor 13.

It will be understood that the charging circuit for the storagecapacitor 13 can be replaced by'a battery (see FIG. la) or other directcurrent source independent of the line 6. In this event, the isolatingtransformer 11, the rectifier bridge l2'and the filtering network 14,16, 17 can be avoided. This expedient is best employed when the spaceavailable for the pulse output device 4 is meager in the region of thewelding zone. in that case, the terminals T+ and T can be connected viarelatively long leads to the DC source (e.g. a battery) which can servea number of output networks 4 and their respective welding stations.

The output side of the discharge network includes a pulse formingtransformer (output transformer 19) which serves to isolate the pulseforming network from the welding system 2, 3 and to inductively couplethe pulse forming network to the latter. The primary winding 19a of thistransformer is bridged across the diode 21 which shunts or shortcircuits the input side of the transformer for passage of pulses of onepolarity while blocking the short circuit and effectively connecting theprimary winding 19a in circuit with the anode-cathode terminals of thecontrolled rectifier 20. The latter functions analogously to a thyratrontube and will be referred to hereinafter as a thyristor.

The secondary winding 19b of the output transformer 19 is bridged acrossthe welding electrode 3 and the workpiece 2 in series with an isolatingcapacitor 22 and a current limiting resistor 23. The pulse transformer19 can be dispensed with, in which case the discharge storage capacitor13 is coupled directly across the electrode 3 and the workpiece 2 by,for example, connecting the L, and L, to output terminals 0' and 0';instead of the output terminals 0, and 0, of the transformer .19. Theuse of an output transformer, however, has the ad vantage that it maybe, as shown, a stepup transformer,

thereby obviating the necessity of designing all of the circuitry of thepulse forming unit 4 with high-voltage output capability.

winding 25a energized via a breakdowndevice 31 which will be describedin greater detail hereinafter.

It will be understood that, in place-of, the-full wave rectifier bridge24, a pair of counterconnected'unidirectional diodes may be employed toeffectively double the output pulse frequency by reversing every otherhalf cycle generated at the transformer 25. The pulse source comprises atransformer 29 whose primary winding 29a is connected to the output sideof the stepdown transformer 8 between the variable inductance 9 and itsfiltering capacitor 10 and the electrodes 2, 3 so that the timing pulsesdelivered to the transformer 29 are in the cadence of the weldingpulses. The output or secondary wind ing 29b of the transformer 29 isconnected to the primary winding 25a of transformer'25 in series withthe voltage-tie pendent switching element or breakdown device 31 such asa glow tube, a zener diode, a voltage stabilizing or VR tube or even atransistor, double-base diode or unijunction transistor.

The control circuit also includes a storage capacitor 33 connectedacross the secondary winding 2% of transformer 29 in series with anadjustable resistor 28 determining the charging rate of the capacitor33. An isolating capacitor 30 is connected between the secondary winding29b and its capacitor 33 and the glow tube 31 while a discharge resistor34 is shunted across the capacitor 30 to form a dischargecontrollingtime constant network therewith. A current limiting resistor 32 is inseries with the glow tube 31 and the primary winding 25a of controltransformer 25.

The primary winding 29a of transformer 29 is connected in series with anisolating condenser 35 and a blocking choke 36. A number of taps areprovided at the transformer 29 to allow the system to accommodatevarious input voltages. In series with the electrode 3 and the weldingtransformer 8 and behind the connection of the control unit 5 therewith,we provide an iron-core choke 37.

OPERATION A. Stabilization of an Altemating Current Welding Arc Theprimary winding of transformer 11a is connected to the alternatingcurrent source 6 via the switch 7 with the alternating current output oftransformer 11 converted into full wave raw-rectified direct current atthe output terminals 12a a and 12b of this bridge. Any perturbations andof this direct current are eradicated by the filter network 14-17 sothat the current supplied to the capacitor 13 on charge is substantiallypure, smooth and ripple-free direct current. Capacitor 13 is thus fullycharged.

The impulsive discharge of the capacitor through the variable resistor18, the primary winding 19a of transformer 19 and the thyristor 20 iseffected at the instant in which a control pulse is delivered to thegate of the thyristor 20 from the control unit 5. This control pulse isapplied immediately after the welding current waveform passes throughthe zero amplitude stage, i.e. immediately after the current amplitudeat the elec trodes has reached null (zero passage).

Thyristor 20 remains conductive for the duration of the discharge of thecapacitor 13 while choke 15, together with the momentary current fiowreversal upon completion of the discharge, ensures quenching of thethyristor 20 and the switching of the latter into its nonconductivecondition. Charging of the capacitor 13 for the next cycle beginsimmediately. The duration of discharge of the capacitor 13 depends uponthe impedance of this capacitor and the resistivity of its dischargenetwork including the impedance of transformer 19, the resistor 18providing a fine adjustmentof the discharge time constant. Best weldingresults have been found when a pulse width of l to microseconds isdelivered by the capacitor and the thyristor 20.

The discharge pulse generated by the storage capacitor and the thyristoris amplified in the transformer 19, attenuated only slightly in thenetwork 22, 23, which blocks DC reverse surges, and applied via leads Land L across the electrode and the workpiece 2, 3. Capacitor 22 isolatesthe transformer 19 from the welding current circuit while the iron-corechoke 37 prevents dissipation of the pulses from the pulse generator 4in the welding current source.

The current pulses superimposed upon the electrode 3 and workpiece 2 mayhave an amplitude of about 10 amperes and, using the step of transformer19, the pulses may have a peak voltage of 300 to 5,000 volts adjustablevia taps or by adjustment of the frequency. The lower value is preferredfor welding in the region of homes and the like which would be adverselyaffected by radio and television interference signals while the uppervoltage ranges may be employed, for example, in automated plasma weldingandcutting installations, in submerged-arc systems and the like. Forthese outputs, the thyristor 20 may be energized with direct currentpulses of a voltage level of 40 to 1,000 volts at currents of 40 to 400amperes.

The welding voltage across the electrode 3 and the workpiece 2 actuallyhas, during the welding process, the substantially rectangular waveformillustrated in FIG. 2a. Immediately after the null transition (zeropassage) of the welding voltage (represented at T of the graph), i.e.directly after quenching of the arc, the voltage pulse reaches itsmaximum amplitude or value. This sharp increase in voltage across theelectrodes with extremely steep flank is sensed by the control circuit 5and triggers at T, a pulse represented at i and occurring directly afterzero passage of the alternating current welding voltage as shown in FIG.2a. This pulse reignites the arc and ensures such reignition at eachcycle. From FIG. 20 it can also be seen that the arc does not extinguishduring the zero passage from the positive half cycle to the negativehalf cycle.

This condition first arises some time after commencement of welding whenthe electrode is relatively hot.

In FIG. 2b, we show the amplitude of the welding voltage of analternating current arc-welding system upon which a direct currentpotential is superimposed in the conventional manner. Thissuperimposition is designed to reduce the duration of the positive halfcycle relative to the negative half cycle (FIG. 2b). The specialsignificance of the present invention in this case will be apparent fromthe fact that also here the pulse i is produced at the precise time T atwhich it is required for reignition of the welding arc and for assuringa stable are even though the period between the zero-passage fromnegative to positive half cycle and the zero-passage from positive tonegative half cycle may be shorter than the period between thezero-passage from positive to negative half cycle and the zeropassagefrom negative to positive to positive half cycle (at which the pulse istriggered).

The alternating current potential across the electrode 3 and theworkpiece 2 is thus used to trigger the control circuit 5 via thetransformer 29 which has the isolating condenser 35 in its primarycircuit to function as a DC-blocking impedance preventing passage of thedirect current component of the welding current through the zero-passagedetection network constituted by the transfonner 29. In addition, theisolating condenser 35 prevents erroneous operation of the pulsegenerator as a result of a perturbation in the DC source. The

blocking choke 36 protects the primary network of the zeropassagedetector 29 from transients.

As noted, the potential across the electrode 3 and the workpiece 2 andthe potential across the primary winding 29a of transformer 29 risesrapidly upon zero-passage of the applied voltage and quenching of theare; consequently, the control storage capacitor 33 is rapidly chargedat a charging time determined-by the impedance of the secondary winding29b and the variable resistor 28. The glow tube 31, which remains in itsnonconductive condition during charge, prevents drain of the capacitor33 during this interval. Thus the voltage across the glow tube 31 alsobuilds up rapidly until its breakdown voltage or threshold is reached.At this point, the breakdown device 31 becomes conductive and apulselike discharge of capacitor 33 is effected through the breakdowndevice 31 and the primary winding 25 of the control-pulse transformer 25and the current limiting resistor 32. The pulse duration continues untilthe time-constant network 30, 34 has its capacitor 30 charged. Thecurrent flow through the primary winding 25a is terminated at thisinstant and the glow tube 31 quenched. The voltage capacitor 30 is bledoff by the resistor 34, thereby preparing the pulse triggering circuitfor the next cycle.

The output of transformer 25 is used to trigger the thyristor 20 overthe full wave rectifier 24 and the adjustable resistor 26, the signalbeing applied to the gate of the thyristor to generate an amplifiedpulse across the electrode 3 and the workpiece 2 as previouslydescribed.

Another embodiment of this invention is shown in FIG. la in which azener diode 131 has replaced the glow tube 30 in the primary circuit ofthe pulse transfonner 125. In addition, the DC source 11, 12, l4, l6 and17 has been replaced by a battery 112. In this embodiment, a pluralityof controllable semiconductive devices (e.g. two solid state controlledrectifiers and 120) are employed. The controlled rectifiers 120 and 120'are poled oppositely to one another while the rectifier bridge 24 isreplaced by a pair of unidirectional rectifiers, i.e. rectifier diodes124 and 124', each connected with a respective secondary winding of thepulse transformer 125 via the load resistors 127, 127 and the variablecurrent limiting resistors 126 and 126'. Otherwise, the circuit appliespulses of alternate polarity across the electrode 3 of the workpiece 2and is desirable when the arc stabilizing pulses must have the samepolarity as the welding half cycle upon reignition. Surprisingly, thishas not been found to be the case in most situations and practicallyidentical stabilization is obtained when the pulses applied across theelectrode 3 and the workpiece 2 are of only one polarity. It isdesirable to choke ofi any reverse current surges of oscillations in thedischarge circuit of the storage capacitor 13 after the generation ofthe pulse and we have found that this is best done by shunting theprimary winding of transformer 19 with a diode 21 (FIG. 1). In thismanner, in spite of the unavoidable inductance phenomenon in the weldingcircuit and the tendency toward oscillation, only single-polarity pulsesare generated, two such pulses being applied during each period of thealternating current weld operation.

B. Ignition of Alternating Current Welding Arc The previously describeddevice may be used, as has been noted, without substantial modificationfor the ignition of welding arcs. Prior to ignition of the are, thewelding voltage applied across the electrode 3 and the workpiece 2 hasthe wave form illustrated in FIG. 3. The voltage rises after zeropassagerelatively slowly in accordance with the sign wave and reaches themaximum T only after a multiple of the time span T T becomes conductivemuch later in the case in which the system is used for the initialignition of the arc than when the glow tube is used to trigger pulsesduring the course of arc welding. The control pulse for the thyristor 20(FIG. 1) and, therefore, the applied pulse across the electrode 3 andthe workpiece 2 occurs, as is schematically illustrated in FIG. 3, at I,is produced only at some time after the zero-passage T of thealternating current voltage, i.e. at T,,; which is very close to thedesirable maximum voltage T at ignition. In other words, at the point Tthe nonload voltage applied by the welding source across the electrode 3and the workpiece 2 suffices to cause breakdown of the glow tube 31 and,therefore, application of the pulse of circuit 4 substantiallysimultaneously with the maximum of the welding'pulse and'ignition.

C. lgnition of Direct Current Welding Arc Aside from the stabilizationand ignition of an alternating current welding are as has been describedabove, the present systernmay be used to ignite a direct current arcsolely with modificatioii of the source as shown in FIG. 4. In FIG. 4,the units 45 and 46 are to be considered identical to the pulse formingcircuit 4 and the triggering circuit 5 described in connection withFlG. 1. In this system, however, a welding current source 38 replacesthe source 1 and comprises a three-phase line connection39 whoseswitch47 energizes the three-phase transformer 40 representeddiagrammatically. A plurality of saturable reactors for adjustablechokes'41are connected in series with the three-phase transformer 40between the latter and a full wave rectifier'bridge'42 connected in theusual manner to the electrode 43 and the workpiece44. The terminals 38aand 38b tap a portion of the input to the transformer 40 off to providethe input for transformer 11. The deflecting transformer 29 isconnectedto. theterminal 38c and 38d bridged across two of the phaseoutput reactors 41. The system illustrated in FIG. 4 has the significantadvantage that with direct current welding sources with fallingcharacteristic, the control element operates only upon ignition and as aconsequence of the low voltage developed across the breakdown 'device.31, the system does not apply control pulses except when reignition isrequired and complete extinction of the arc has occurred. The ignitionoperationis carried out as previously described.

The present process for stabilizing and igniting welding arcs should notbe construed in a narrow sense and is intended to include arc-weldingwith or without protective gases, with destructible or indestructible(consumable or nonconsuma- -ble) electrodes, submerged arc-welding, arcdeposition coating, and the like. It also applies to are cutting, plasmawelding, plasma coating,plasma cutting, plasma planing and plasma spraydeposition. in plasma systems, the plasma stream may be consideredequivalent to the are described.

, The improvement described and illustrated is believed to admit of manymodifications within the ability of persons skilled in the art, all suchmodifications being considered within the spirit and scope of theinvention except as limited by the appended claims.

We claim: 1

l. A system for the stabilization and ignition of an are generatedacross an arc gap by the application of an arc forming currentthereacross from a source of alternating current, said system comprisinga pulse generating circuit connected across said gap and including aprimary storage capacitor, means for charging said primary storagecapacitor, a discharge circuit for said primary storage capacitorconnected across said gap, and a triggerable semiconductor switch inseries with said primary storage capacitor and enabling the chargingthereof in a nonconductive condition of said switch and discharging saidcapacitor in a conductive condition of said switch to apply a pulseacross said gap; and a triggering circuit connected with said source andwith said switch for triggering same to apply said pulse across saidgap, said discharge circuit including a stepup transformer having asecondary winding connected across said gap, and a primary windingconnected in series with said switch and said primary storage capacitor,said triggering means including a detector transformer having a primarywinding energized by said source and a secondary winding, a secondarystorage capacitor connected across said secondary winding ofsaid'detector transformer, an adjustable charging resistor between saidsecondary winding of said detector transformer and said secondarycapacitor, and a secondary discharge circuit for said secondarycapacitor producing controlled pulses for said switch, said secondarydischarge circuit comprising a pulse transformer having a primarywinding and a secondary winding, a voltage-responsive breakdown deviceconnected in series with said secondary capacitor and the primarywinding of said pulse transformer, a time-constant network for quenchingsaid breakdown device upon the elapse of a predetermined conductiveinterval thereof, and rectifier means energized by the secondary windingof said pulse transformer and connected with said switch for triggeringsame.

2. The system defined in claim 1 wherein said switch is a solid-statecontrolled rectifier having its gate connected to said rectifier means.

"3. The system defined in claim 2 wherein said time-constant networkincludes a condenser connectedv etween said secondary capacitor and saidbreakdown de ce and a. resistor shunting said condenser.

'4. The system defined in claim 2, further comprising a directcinrrent=blockingisolatingcondenser in circuit with the primary windingof said detector transformer between the latter and said source.

5. The system defined in claim 2, further comprising an iron-core chokeconnected between said source and said gap 6. The system defined inclaim 2 wherein said breakdown device isa glow tube. t

'7. The system defined in claim 1 wherein said discharge circuit furthercomprises a diode bridged across said primary winding of said stepuptransformer, said switch being a solidstate controlled rectifier.

8. The system defined in claim -l,whe rein said means for charging saidprimary storage capacitor includes direct cur.- rent input meansconnected across said primary storage capacitor and a choke connected inserieswith said primary storage capacitor and to said input means.

9. The system defined in claim 8 wherein said input means.

- capacitor. 7

10. A system for the stabilization of an alternating current welding orplasma arc and for the ignition of an alternating current or directcurrent welding or plasma are generated across the arc gap produced atleast in part by an electric source having an output with a zero-passageand for generating a pulse superimposable upon the arc gap for aduration of 0.8 to 20 microseconds and adapted to induce the formationof said are in the cadence of the mains voltage, at ignition on theturning point and at welding in said zero-passage, said systemcomprising:

a pulse generating circuit connected across said gap and including aprimary storage capacitor, means for charging said storage capacitor, adischarge circuit for said storage capacitor connected across said gap,and a triggerable semiconductor used as quick break switch in serieswith said storage capacitor and enabling the charging thereof in anonconductive condition of said switch and discharging said storagecapacitor in a conductive condition of said switch to apply a pulseacross said gap; and

a triggering circuit connected with the output of said source and withsaid switch for triggering said switch to apply said pulse across saidgap comprising a secondary storage capacitor, means for charging saidsecondary capacitor and a secondary discharge circuit for said secondarycapacitor producing controlled pulses for said switch, said secondarycircuit comprising a voltage responsive breakdown device connected inseries with said secondary capacitor and an assembly for quenching ofsaid breakdown deviceupon the elapse of a predetermined conductiveinterval thereof, and rectifier means connected with said switch fortriggering same, said triggering circuit including a pulse transformerhaving a primary winding connected in series with said secondarycapacitor and with said breakdown deviceand a secondary windingenergizing said rectifier means.

rectifier means.

12. The system defined in claim 10 wherein said discharge circuitincludes a stepup transformer having a secondary winding connectedacross said gap, a primary winding connected in series with said switchand said primary storage capacitor, and a freewheeling rectifier bridgedacross said primary winding.

13. The system defined in claim 12 wherein said triggering circuitfurther includes a detector transformer having a primary windingenergized by said source and a secondary winding connected with saidsecondary capacitor.

14. The system defined in claim 10 wherein said quenching assembly is atime-constant network including a further

